Problem: Solve for $y$ : $y - 18 = -3$
Answer: Add $18$ to both sides: $ \begin{eqnarray} \\ y - 18 &=& -3 \\ \\ {+18} && {+18} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{-18 + y} &\hphantom{=}& \hphantom{-3} \\ y &=& -3 {+ 18} \\ \end{eqnarray} $ Simplify. $ y = 15$